1. Technical Field
The present invention relates to an anti-lock brake system (wheel slide protection) for vehicles. More specifically, the invention relates to an anti-lock brake system for trailers which can perform the function of intermittently relaxing a braking force applied to the wheels of a trailer that is being hauled by an engine.
2. Background Art
Brake systems of railway vehicles generate a braking force on the basis of a brake command originating at a motor-powered car, and the braking force is applied to both the motor-powered car and to one or more trailers being hauled by the engine. In the art, different kinds of signals are used as commands in an air brake system, for example, a pneumatic signal by pressure variation in compressed air, an electric signal, and the concurrent use of pneumatic and electric signals, and so on.
These kinds of brake systems comprise an anti-skid system for intermittent relaxation of the braking force applied to the wheels. The anti-skid system comprises a skid detecting unit, a brake cylinder, and an anti-skid valve. The skid detecting unit detects the skid of the wheel. The brake cylinder is pressurized by compressed air and generates a braking force which is applied to the wheels. The anti-skid valve decreases a pressure of compressed air which is provided to the brake cylinder. The anti-skid valve has a function of relaxing the braking force intermittently by controlling the pressure of compressed air in accordance with signals sent from the skid detecting unit.
Ordinarily, the anti-skid valve comprises at least one solenoid valve. A solenoid valve decreases the pressure of compressed air within the brake cylinder by using magnetic power generated by energizing solenoids.
FIG. 15A is a circuit diagram showing the configuration of the pneumatic circuit of the anti-skid valve disclosed in Japanese Patent document, JP 3209288 B. FIG. 15B is a circuit diagram showing the phases of the anti-skid valve in the prior art. As shown in FIG. 15A, the anti-skid valve in the prior art comprises two main valves and two pilot valves. One main valve is a normally-open, two-position, two-way valve and is referred to as “lockout valve” (lockout valve 2112A). The other main valve connected serially to the lockout valve is a normally-closed, two-position, two-way valve and is referred to as “release valve” (release valve 2112R). Both of the pilot valves (2111A and 2111R) are normally-closed, two-position, three-way solenoid valves and each one of the pilot valves functions as a pilot valve for a corresponding main valve. The anti-skid valve in the prior art is operated by a control method as shown in FIG. 14B. That is, both of the pilot valves are energized (FIG. 14B: region II and IV) in a case that the braking force is relaxed. Then the lockout valve is closed and the release valve is opened. According to this operation, compressed air is not fed into the brake cylinder and the compressed air within the brake cylinder, which is released through the release valve is eventually exhausted. Thus the braking force is relaxed. Also, the pilot valve of the lockout valve is energized and the pilot valve of the release valve is de-energized (FIG. 14B: region III and V) in a case that the braking force is maintained. Similarly, both of the two pilot valves are de-energized (FIG. 14B: region VI) in a case that the braking force is re-applied.
There are some disadvantages in the above described control method of the prior art. According to the control method in the prior art, it is necessary for both the pilot valves to be energized in the case that the function of relaxing the braking force is performed. As a result the system consumes a large amount of power. Another disadvantage of the prior art is to do with all three ports of the anti-skid valve being connected to each other (this is referred to as “all ports open” phase). The “all ports open” phase occurs when the pilot valve of the lockout valve is de-energized and the pilot valve of the release valve is energized. This phase does not occur in the ordinary way, but may occur as a result of a malfunction of control circuit.
A power supply with a stable output voltage is required for operating the solenoid valves of the anti-lock brake system. However, it is difficult to obtain stable output voltage in trailers of railway vehicles. A brake system which comprises power supply (secondary battery) in the vehicle has been developed to overcome the problem. In the prior art, a generator, which generates power in response to the rotation of the wheels, is installed in the vehicle to charge the secondary battery without an external power supply.
As described above, the anti-skid valve consumes power continuously while the anti-lock brake system is in an anti-lock operation mode. Therefore, there is a possibility that the battery is over-discharged in a case that the vehicle has been in an anti-lock (anti-skid) operation state for more than a certain duration with a concomitant increase in power consumption which results in an increase of costs for running power converters or batteries in railway vehicles. Thus, a brake system with a low power consumption is required for railway vehicles with generators; railcars which travel through unelectrified regions; and hybrid motorcars driven by electric motors.
In the anti-lock brake system of the prior art, the secondary battery is charged by a generator which is installed in a vehicle. In this case, the secondary battery cannot be charged when the wheels are stopped because the generator cannot generate power when the wheels are stationary. Therefore, there is a possibility that the secondary battery becomes over-discharged in a case that the vehicle has been stationary with the secondary battery being over-discharged. When the vehicle starts rolling, the secondary battery is charged by the generator. However, the brake system cannot operate in a case that the remaining capacity of the second battery is not sufficient to operate the brake system.
As disclosed in Japanese Patent Application JP 2000-108864 A, a lead acid battery is conventionally used as a power supply for the brake system installed in a vehicle. Generally, the lead acid battery has many problems when used as a power supply for the brake system. Firstly, the lead acid battery has a short lifespan when used for charging/discharging as well as a lower level of reliability. Secondly, it is necessary for a lead acid battery to be large in order to obtain the necessary characteristics for use as a power supply for the brake system because the ratio of its energy density to its power density is small. Thirdly, the capacity of the lead acid battery is affected by temperature, with a decrease in capacity as the temperature lowers.
The electric double layer capacitor is developed to overcome the above problems. FIG. 18 shows a perspective view of an electric double layer capacitor and its mounting hardware in a prior art. FIG. 20 is a sectional view of the capacitor unit cell of the electric double layer capacitor in the prior art. As shown in FIG. 18, the electric double layer capacitor for vehicles in a prior art comprises rondure capacitor unit 3050 and mounting hardware 3051 for mounting rondure capacitor unit 3050 on a vehicle. Mounting hardware 3051 is C-shaped and comprises two mounting portions 3053 on its two ends, which extend outwards. Mounting hardware 3051 also comprises three mounting portions 3052 which extend outwards, at positions by which the circle of the ring is divided into three equal parts. To mount the electric double layer capacitor in a prior art on a vehicle, at first, mounting hardware 3051 is carried on the circumference of rondure capacitor unit 3050, and then the capacitor unit is mounted using screws on a desired position of the vehicle through mounting portion 3053.
FIG. 20 shows the structure of the basic unit cell of the electric double layer capacitor in a prior art. As shown in FIG. 20, basic unit cell 3055 of rondure capacitor unit 3050 comprises a pair of electrodes 3058, separator 3057, a pair of collectors, and seal rubber 3056. More specifically, electrode 3058 comprises powdered activated carbon electrode and sulfuric acid solution electrolyte. Two electrodes 3058 face each other via separator 3057. Two collectors 3059 are located so as to sandwich two electrodes 3058, and the periphery of the two electrodes 3058 is sealed by seal rubber 3056.
FIG. 21 is a sectional view of the electric double layer capacitor in the prior art. As shown in FIG. 21, rondure capacitor unit 3050 is configured as follows. A plurality of basic unit cells 3055 is laminated parallelly to the bottom of the case. Laminated unit cells 3055 are covered by a can case which has an opening on its upper side and two metal plates on its bottom. The edge of the opening is angled inwards to prevent the metal plate from dropping. Each metal plate has a lead terminal. The lead terminal of the positive electrode extends outwards via a through hole, which is made at the bottom of the insulated case. A boss is made at the edge of the through hole to prevent the metal plate of the positive electrode from coming into contact with the metal plate of the negative electrode. Similarly, the metal plate of the negative electrode also has a lead terminal which extends outwards.
For use as a power supply for vehicles, it is necessary that an electric double layer capacitor has the electronic characteristic of a high breakdown voltage. To obtain a high breakdown of voltage, aqueous electrolyte is preferable for the electrolyte of the electric double layer capacitor because it has the advantage of managing a serial connection. It is noted that a structure is necessary to carry out the function of pressing the capacitor from top to bottom.
Further, a more important characteristic of the electric double layer capacitor used as a power supply for vehicles is that the capacitor is resistant to adverse environmental conditions. Specifically, there exists the problems of degradation of electric or mechanical characteristics caused by (1) mechanical vibration of the vehicle when rolling, (2) wide range of temperature variation, or (3) pollution by contaminants. Different electric double layer capacitors are developed to overcome the problems. However, the structure disclosed in Japanese Patent Application JP 2000-3838 A has the problem of a low breakdown of voltage because the structure employs an organic electrolyte. Also the structure disclosed in Japanese Patent Application JP 2002-50552 A has the problem of vibration proof because it has no fixed structure of electrodes. Thus, electric double layer capacitors in the prior arts do not have the necessary capabilities for effective usage.